DISTANCIA ENTRE EJES MAS ALEJADOS RADIO DE GIRO MÍNIMO

6.4.2.1.1 LoRaWAN™

LoRaWAN™ is a LPWAN specification intended for wireless battery-operated devices in several network areas such as regional, national or global [195]. In fact, LoRaWAN™ provides a bidirectional communication, mobility and localization services avoiding complex local installations. By this way the communication of several devices will be comfortably with control centre.

The LoRa architecture is a star topology where the end devices communicate with several gateways which communicate with network server system. In fact, this kind of network is covering little areas with local gateways to change the protocol and physical medium in order to connect with servers in the backend by means of Internet Protocols (IP). In fact, the gateways have to be connected to the network server through IP connections, nevertheless end terminals use single hop wireless communication to one or many gateways. This feature can allow a bi-directional communication although it supports operation such as multicast enabling software upgrade or other mass distribution messages. One of the important aspects of LoRa is the possibility to support software upgrades and mass distribution messages.

The communication among end-devices and gateways is by means of different frequency channels and data rates. The selection of the data rate depends on the communication range and message duration. LoRa can communicate with different data rates and it will not interfere with others and create a set of virtual channels. This fact is due to the spread spectrum technology [196] which increases the capacity of the gateway. As mentioned before the data rate is under the limits of a LPWAN communication, this is not a big speed communication in the channel but can help to optimize the battery life of the end-devices and the network capacity. Although the server is in charge of to manage the data rate and radio frequency output for each device.

LoRaWAN™ can operate devices in a regional, national or global network and besides this technology has the possibility to establish bi-directional communication, mobility and localization services. There are several conditions in order to fulfil a robust communication in everywhere with few information. These conditions are indicated as follow.

• Long battery life.

• Wide area connectivity characteristics, allowing for out of the box connected solutions. • Low cost chipsets and networks.

This set of requirements provides to end user and business developer a ready technology to enabling the roll out of IoT due to the cost and integration devices in a LoRaWAN™ network is easy in comparison with other kind of networks. In fact, there are several classes of end-point devices to establish different solutions as follow.

• Class A. Bi-directional end-devices. Tis devices are prepared for bi-directional communication whereby each equipment has an uplink transmission which is followed by two short downlinks receive windows. These devices need a low consumption due to require downlink communication from the server after to send an uplink transmission.

• Class B. This kind of device opens extra receive windows at scheduled times. This fact will allow the server to know when the end-device is listening in the channel.

• Class C. In this case the device is opened only it will be closed when the device transmits some information through the channel.

As an example, regarding to the AFL algorithm presented previously the best communication skill should be the class A because the consumption is lower than other classes and maybe it will be used properly in overhead DFPIs. As mentioned before this kind of DFPIs can be supplied by a small battery. According to [197] it is not necessary to establish an important infrastructure in order to deploy a device with LoRa capability to communicate. Additionally, it is important to remark that LoRa can manage several millions of devices with few data per day [198] and cover an important extension of territory [199]. It is enough for DFPIs applications, although the temperature can affect considerately to the signal [200].

Nowadays one important aspect of this network is the cybersecurity. Previously LoRaWAN™ has several encryption layers such as unique network key (EUI64) to ensure security on network level, unique application key (EUI64) in order to ensure end to end security on application level and device specific key (EUI128) [195].

6.4.2.1.2 Sigfox

Unlike LoRa, Sigfox is not a standard, it is a French IoT provider. Its network is a backend where the different devices launch the data and it manages the message transference by means of a http request to a presetting backend.

This situation provides to the sensors developers the possibility to integrate comfortably the radio module in these devices. The Sigfox network is based on star topology which requires a mobile operator to carry the generated traffic. The signal can also be used to easily cover large areas and to reach underground objects. This is a technology Ultra-NB-IoT which works with radio bands between 868 MHz in European region and 902 MHz in USA.

Sigfox transmits data by means of a standard radio transmission method called Binary Phase-Shift Keying (BPSK). The modulation of this standard is very slow due to the speed is 300 bps. Although this modulation rate can allow to get a great range using few base stations. As an example, it is important to remark that in USA this system modulates at a higher rate due to in the normative FCC part 15 the maximum time a transmission can be on the air is 0.4 seconds [201]. It is important to remark that Sigfox has developed the cybersecurity concept in their solutions through IT security, secure software and architecture [202] as in the case of LoRa.

6.4.2.1.3 NB-IoT

NB-IoT is a LPWAN radio technology standard designed for the IoT which has been developed to link several devices and services to be connected through cellular telecommunications bands. NB-IoT has been released by 3rd _{Generation Partnership Project (3GPP) in order to provide extended coverage and low}

energy consumption for low cost devices [203]. This development has only required a low-cost hardware update in the Long Term Evolution (LTE) devices in order to reduce the battery consumption and minimize the signalling. It is important to remark that NB-IoT has a fast connection and can send 12 bytes per day. Nowadays the NB-IoT deployment is quickly increasing then this technology is dominating the LPWAN [204]. This kind of networks can support the firmware and software transmission and other functions such as task updates or commands towards an important number of devices due to its optimised data transfer. As in the case of LoRa and Sigfox, NB-IoT has been thought for use as a low power consumption which can be deployed into existing cellular network architecture in an indoor and outdoor range supporting more than 100,000 connections per cell. NB-IoT supports security by two-way authentication and strong interface encryption. The possibility to use the established network 4G or 5G and its future evolutions will provide a robustness network in order to deploy IoT devices around the networks such as the electrical system.